In a semiconductor manufacturing process, various kinds of semiconductor manufacturing apparatuses or semiconductor inspection apparatuses have been used. For instance, a plasma processing apparatus performs, e.g., an etching process or a film forming process on an object to be processed by generating a plasma.
Such processing apparatuses include a plurality of parameters for controlling or monitoring operation states thereof, and perform various processes under an optimum condition by controlling or monitoring the parameters.
As parameters employed in, e.g., a plasma processing apparatus performing a film forming process or an etching process on an object to be processed such as a semiconductor wafer or a glass substrate, there are controllable parameters such as a flow rate of processing gas introduced in a processing chamber, a pressure in the processing chamber, a high frequency power applied to at least one of electrodes disposed, e.g., facing to each other in the processing chamber (hereinafter, referred to as control parameters).
Further, there are parameters such as optical data obtained through, e.g., plasma spectrum analysis for understanding a plasma state excited in the processing chamber, and electrical data, e.g., a high frequency voltage and current of a fundamental and harmonic wave based on the plasma (hereinafter, referred to as plasma reflection parameters).
Moreover, there are parameters such as capacity of a variable condenser under a matching condition of a matching unit provided for an impedance matching when a high frequency power is applied to the electrode in the processing chamber, and a high frequency voltage measured by a measurement area in the matching unit (hereinafter, referred to as apparatus status parameters).
When the plasma processing apparatus performs a process, the control parameters are set to optimum values, so that the plasma processing apparatus can be controlled to perform the optimum process by monitoring the plasma reflection parameters and the apparatus status parameters by detectors thereof all the time. However, since there are tens of kinds of such parameters, it is very difficult to exactly pinpoint the cause when an abnormality of the operation status is noticed.
Meanwhile, there has been proposed in, e.g., Japanese Patent Laid-open Publication No. H11-87323 a processing apparatus and a monitoring method thereof wherein a plurality of process parameters of a semiconductor wafer processing system are analyzed, and variations in process characteristics and system characteristics are detected by statistically correlating the parameters as data in an analysis.
Moreover, there is a method for estimating an operation status wherein the parameters are taken as analysis data and consolidated to a fewer number of statistical data by using a principal component analysis method which is one of multivariate analyses, so that the operation status of the processing apparatus is monitored based on the fewer number of statistical data.
In such conventional methods, a status abnormality of the plasma processing apparatus is detected by calculating indexes such as a sum of residual squares, a principal component score and a sum of principal component score squares from, e.g., a statistical analysis result such as the principal component analysis. Further, in case an abnormality is determined, the cause thereof is studied based on the indexes, and the status of the plasma processing apparatus can be ameliorated by, e.g., performing a wet cleaning if desired, or carrying out replacement of consumable parts or detection devices (sensors).
However, when the maintenance such as the wet cleaning described above is carried out, even when there is no real abnormality occurring in the plasma processing apparatus itself, a large error (hereinafter, referred to as a shift error) can be detected in the indexes such as the sum of residual squares (residual score), thereby decreasing the accuracy of the abnormality detection. One of the causes of the above phenomenon is speculated that trend of the status of the plasma processing apparatus is changed whenever the wet cleaning is carried out.
In case the trend of the status of the processing apparatus is changed due to the wet cleaning as described above, even when the status of the plasma processing apparatus is normal, there may develop a great variation in the indexes such as the sum of residual squares and the like. As a result, it is impossible to check whether or not the status of the plasma processing apparatus is abnormal. Therefore, there may occur a unique problem of the plasma processing apparatus wherein an accuracy of abnormality detection and an accuracy of prediction are decreased.